Abstract:The influence of hot swaging (SW) and annealing treatment on microstructure and mechanical properties of commercially pure titanium produced by investment casting was evaluated. The as-cast samples showed a typical microstructure consisting of a variety of α-morphologies, while the hot swaged samples exhibited a kinked lamellar microstructure. Annealing at 500 °C did not significantly change this microstructure while annealing at 700 and 870 °C led to recrystallization and formation of equiaxed microstructures. The cast bars exhibited a typical hard α-layer in near-surface regions with a maximum depth and maximum hardness of 720 μm and HV_0.5 660, respectively. Due to SW, the tensile strength of the as-cast material drastically increased from 605 MPa to 895 MPa. Annealing at 500 °C decreased the tensile strength slightly from 895 to 865 MPa while annealing at 700 °C led to a further pronounced drop in tensile strength from 865 to 710 MPa. No additional decrease in tensile strength was noticed with increasing the annealing temperature from 700 to 870 °C. The true fracture strain of the as-cast and hot swaged samples was in the range of 0.05 to 0.12, while the annealed samples showed values in the range of 0.25 to 0.53. In addition, the as-cast and hot swaged samples revealed a brittle cleavage fracture surfaces. However, the annealed samples showed a transgranular ductile fracture with formation of dimples.

Key words: pure titanium; investment casting; swaging; thermo-mechanical processing; mechanical properties